Why every Crosslight puzzle has a solution

Each Crosslight board starts from an all-off grid. The game applies a fixed set of legal moves to create the starting pattern. Because every move is reversible, applying that same set again clears the board. There is no random arrangement that might accidentally be impossible.

A tiny model

Think of an off tile as 0 and an on tile as 1. A move flips selected values: 0 becomes 1 and 1 becomes 0. Two flips on the same tile cancel. For a whole board, each move is a pattern of flips covering the selected tile and the neighbours that exist within the grid.

If a tile is touched by three moves it ends up flipped once overall. If it is touched by four moves it ends where it started. Only whether the number is odd or even matters. That is why changing the order of a fixed set of moves cannot change the final board.

Construction is not a shortest-path claim

The move set used to construct a board gives one way to solve it. It does not automatically tell us the fewest possible moves. A different combination can sometimes produce the same overall pattern. Crosslight therefore shows your move count without labelling it a world record, optimal score or ranked result.

The five puzzles use fixed starting arrangements. Restarting a puzzle returns to the same pattern, making it possible to compare approaches. The game has no daily clock or server-side competition, so changing the date does not generate a new challenge.

How you can check the rules

1. Start a puzzle and select a tile twice. Check that the board is restored.
2. Restart and select two different tiles. Compare with the reverse order after another restart.
3. Test a corner to see that the effect does not wrap around to the opposite edge.
4. Use Undo to verify that it restores the previous board and move count.

These simple checks explain more than the colour of the lights. They show the properties that allow the row-by-row solving method to work.

A deliberately small browser game

The board and your move history exist in the current browser page. There is no player account or remote score service. Refreshing resets the attempt. The surrounding rules and guides are normal pages, so you can read them independently of the interactive board.

Crosslight is Olav Games' implementation of a cross-toggle logic puzzle. It is built for a short, untimed break with keyboard and touch controls. Play a puzzle and try predicting what two moves will do before making them.